[whatwg] Canvas arcTo

Kristof Zelechovski giecrilj at stegny.2a.pl
Mon Jul 2 16:43:58 PDT 2007

The questioned wording is correct: a straight line has infinite radius and
thus does not match the requirement if the radius is finite.

-----Original Message-----
From: whatwg-bounces at lists.whatwg.org
[mailto:whatwg-bounces at lists.whatwg.org] On Behalf Of Philip Taylor
Sent: Monday, July 02, 2007 1:42 PM
Subject: [whatwg] Canvas arcTo

"If the point (x2, y2) is on the line defined by the points (x0, y0)
and (x1, y1) then the method must do nothing, as no arc would satisfy
the above constraints." - why would no arc satisfy the constraints? If
P0, P1, P2 are collinear and non-coincident, then (I think) any of the
(infinitely many) circles which have the given radius and touch
tangential to the line P0->P2 will satisfy the constraints (i.e. being
tangential to P0->P1 at some point and to P1->P2 at some point).


"Negative or zero values for radius must cause the implementation to
raise an INDEX_SIZE_ERR exception." - why not allow zero? You just get
an arc at P1 with zero length, with the start and end tangent points
both at P1, so the effect would be a straight line from P0 to P1,
without needing to handle it as a special case. Safari works like

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